This invention relates to a process for converting an acyclic monoolefin to its corresponding terminal organonitrile compound by reacting the monoolefin with hydrogen cyanide (HCN) in the presence of zero-valent nickel, a phosphite ligand, and a Lewis acid promoter.
Hydrocyanation catalyst systems, particularly pertaining to the hydrocyanation of olefins, are well known in the art. For example, systems useful for the hydrocyanation of butadiene to form pentenenitrile (PN) and for the subsequent hydrocyanation of pentenenitrile (PN) to form adiponitrile (ADN), are known in the commercially important nylon synthesis field. The hydrocyanation of olefins using transition metal complexes with monodentate phosphite ligands is well documented in the prior art. See for example U.S. Pat. No. 3,496,210, 3,631,191, 3,655,723 and 3,766,237; and Tolman, C. A.; McKinney, R. J.; Seidel, W. C.; Druliner, J. D.; and Stevens, W. R.; Advances in Catalysis, 33, 1, 1985. The hydrocyanation of activated olefins, such as conjugated olefins (e.g., butadiene and styrene) and strained olefins (e.g., norbornene), proceeds without the use of a Lewis acid promoter, while hydrocyanation of unactivated olefins, such as 1-octene and 3-pentenenitrile, requires the use of a Lewis acid promoter. Teachings regarding the use of a promoter in the hydrocyanation reaction appear, for example, in U.S. Pat. No. 3,496,217. This patent discloses an improvement in hydrocyanation using a promoter selected from a large number of soluble metal cation compounds. U.S. Pat. No. 3,496,218 discloses a nickel hydrocyanation catalyst promoted with various boron-containing compounds, including triphenylboron and alkali metal borohydrides. U.S. Pat. No. 4,774,353 discloses a process for the preparation of dinitriles, including ADN, from unsaturated nitrites, including PN, in the presence of a zerovalent nickel catalyst and a triorganotin catalyst promoter. U.S. Pat. No. 4,874,884 discloses a process for producing ADN by the zerovalent nickel-catalyzed hydrocyanation of pentenenitriles in the presence of a synergistic combination of promoters selected on the basis of the reaction kinetics of the ADN synthesis. U.S. Pat. Nos. 5,233,058 and 5,286,825 disclose the nickel-catalyzed hydrocyanation of perfluoroalkyl ethylene and other partially fluorinated olefins. U.S. Pat. No. 5,087,723 discloses nickel-catalyzed hydrocyanation of penteneoates. In each of these cases, the catalyst and promoter are dissolved in the reaction medium, providing an essentially homogeneous reaction environment (i.e., everything is soluble). The homogeneous nature of this reaction system makes it difficult to recover the catalyst and promoter for reuse. Whereas practical methods for recovery of nickel catalyst are known (see, for example, U.S. Pat. No. 3,773,809), recovery of promoters remains a difficult problem. U.S. Pat. No. 3,846,474 discloses that the addition of aluminosilicate zeolites to a nickel-catalyzed zinc chloride-promoted hydrocyanation reaction of 3-penetenenitrile may improve catalyst utility and product distribution.